Upholstered furniture is generally covered with leather, vinyl, and fabric. A significant part of the manufacturing cost of furniture is the cost of cutting the cover. Most inexpensive furniture is covered with vinyl or plain fabric or fabric with a small overall pattern. When plain fabric or fabric with a small overall pattern or vinyl is used, it can be cut by placing one layer on top of another, building a stack that is then cut at one time. For this kind of production, automatic machines are known that can stack the fabric or vinyl and then, using a computer guided knife or any suitable cutting means, cut the stack into the required pattern pieces.
More expensive furniture uses fabric that must be matched when applied. The most complicated matching is required with floral patterns. Examples of matching are (1) a stripe that starts at the lower back of a sofa and continues up the back, over the top, down the seat back, across the seat, and down the front to the bottom; (2) each cushion has a flower centered thereon; or (3) trees or animals that are larger than a single piece of fabric in the furniture and which appear to flow across two or more pieces.
Matched fabric is typically manufactured by weaving, knitting, or printing. Unfortunately, as fabric is manufactured, it must pass over many rollers. As a result of the manufacturing process, fabric typically has skew (i.e., the filler or yarn going from one edge to the other across the web is not perpendicular to the length of the fabric) or bow (i.e., the filler yarn is not straight) or both. Moreover, the fabric is typically printed with a printing cylinder or by screen printing. With either method the repeat of the pattern is not consistent. Even if the repeat was originally perfect, the fabric stretches as it is processed. Accordingly, the manufactured fabric typically differs considerably from the ideal in terms of skew, bow and repeat. The fabric may also have other defects including but not limited to dropped threads, holes, and printing defects. Because of these many defects, matched fabric cannot be stacked with any reliability of pattern match and therefore must be cut one layer at time.
The most common method for cutting matched fabric is as follows: The matched fabric is first spread on a cutting table. A highly trained operator places (nests) the individual templates of the pattern on the fabric in the appropriate places so that after cutting, sewing, and upholstering the furniture, the pattern on the furniture matches. After all of the individual templates of the pattern are in their proper place, the operator marks with chalk around each template. The pattern templates are then removed and the fabric is cut with a rotary knife or scissors. An extension of the above described cutting method furnishes the operator with a miniature layout diagram of the total pattern for a perfect fabric as a guide to a more efficient nest, i.e. the nest which requires the least amount of fabric. This layout diagram is referred to as an initial nest.
One method of producing these miniature layout diagrams (initial nest) is as follows: Each fabric is first categorized into 15 to 20 general types. Examples are: regular (the stripe or pattern runs down the length of the fabric), railroad (the stripe or pattern runs across the width of the fabric), railroad center design (the pattern has its top pointing across the fabric and there is one pattern in the center of the web), railroad side by side (the pattern has its top pointing across the web and there are two pattern repeats across the web) and regular three repeat (the top of the pattern is pointing down the length of the web and there are three repeats down the web). After this initial sorting, each repeat distance is then added within each initial category. There are many combinations using this or other similar methods but the specific pattern (flowers, birds, prints etc.) does not have to be considered. Next, miniatures of each template in a cutting pattern are drawn to scale. These miniatures are then arranged in an appropriate layout and a photograph is taken.
Computer programs to assist an operator with producing the initial nest have become available in the past few years, for example the marking system marketed by Micro Dynamics, Dallas, TX. Each full size pattern template for each specific furniture style is entered into the computer using a digitizing tablet, optical scanner, computer automated design (CAD) drawings, or other appropriate means. A group of lines, both horizontal and vertical, that represent the fabric pattern, along with scale miniatures of each piece of fabric to be cut, are displayed on the computer display. The miniatures are displayed in a random pattern outside the area of the display representing the fabric pattern. The operator, using a pointing device or other input device such as a keyboard, picks the first pattern template and places it on the grid lines representing the fabric. The computer program assists the operator in placing the pattern templates on the grid by forcing the match point of the pattern template to the intersection of the grid lines. After all of the miniatures are placed in their appropriate place, a permanent record is made and a hard copy of the layout is produced. The outline of each pattern template along with its appropriate placement, in digital form, may also be used to generate cut data for a computer guided cutting machine.
Most computer guided fabric cutting machines include a brush table. The brush table comprises brush bristles standing on end pointing upward. A motor driven reciprocating knife is carried above this table by a gantry. This gantry has both x (longitudinal) and y (across the web) axes. These axes are generally driven by servo motors interfaced to a computer numerical controller. After one or more layers of fabric is stacked on the brush table, a layer of plastic film is applied to the top of the stack. A vacuum is applied to the underside of the plastic film through the brush table to compact and hold the fabric stack while the knife reciprocates up and down through the fabric stack and into the brush table. The simpler machines have a stationary brush table. More expensive machines utilize a conveyorized brush table and include a conveyor section to stack the fabric while the knife is cutting a previous template. Some machines include an off-load section of conveyor table so that cut pieces can be removed while the knife is still cutting. All conveyorized machines index in sections equal to the length of the actual cutting area.
If the fabric to be cut is plain, the above described machines may be used. If matched fabric was perfect, this type of machine could also be used, because the pattern layout generated by the computer aided marking system would perfectly fit each piece of fabric being cut. However, since matched fabric typically contains the imperfections described above, these machines cannot be used.
One method to enable the above mentioned cutting machines to cut matched fabric is as follows: The total pattern for a given style of furniture is studied. Each major individual piece of the pattern (for example, the seat bottom and back) is placed on a fabric pattern representation and then its most closely related small fabric pattern templates are nested around each major template. In theory, since the pattern repeat is only off by a small amount in any small area, each major piece and its most closely related smaller pieces will match to a fairly acceptable degree.
After this nesting is complete, it is used to guide the cutting machine. The cutting machine instructions include a move by the cutting knife, to the center of the fabric pattern for each major nested group. After this move to the center of the group, a stop instruction is inserted to cause the cutting machine to stop. Once stopped, the machine operator can visually check to see if the stopped cutting machine is in fact at the center of the fabric pattern. If not, then the machine operator can move the cutting machine, using a joy stick or jog buttons, so that the center of the pattern nest coincides with the center of the pattern. This manual move of the machine may be used by the computer when the next nested group of pattern templates is cut. A system which implements the above described method is commercially available as the Model E95.3 marketed by Lectra Systems, Marietta, Ga.
Unfortunately, the above described method and system can only cut fabric accurately if the only fabric defects are pattern repeat errors; i.e. the repeat distance varies. This method cannot correct for other types of fabric defects such as bow, skew, dropped threads, holes or printing defects.
Some newer equipment such as the Model E95.3 with Video Option marketed by Lectra Systems, Marietta, Ga., also mounts a video camera on the cutting gantry. The live video signal is mixed with a digital image of the template of the pattern to be cut in this area of the fabric and displayed, on a computer screen. An "X" is placed at the cutting knife's location. This aid helps the machine operator see the fabric better and move the cutting machine so that the center of the pattern nest coincides with the center of the pattern. However, this live camera only permits the operator to see the fabric at the cutting knife's location so that direct visual observation at the cutting knife is not necessary.